This invention relates to a speed reducer for reducing the rotation of an input member and transmitting the reduced rotation to an output member.
As a speed reducer of the type in which an input member and an output member are arranged coaxially to transmit the rotation of the input member to the output member at a relatively high reduction rate, there is known a differential gear device having planet gears.
Such a differential gear type speed reducer is made up of a large number of parts including a plurality of gears. Thus, it tends to be large in size and costly.